1. Field of the Invention
The present invention relates to an image sensing apparatus and imaging system.
2. Description of the Related Art
These days, image sensing apparatuses such as a CCD image sensor and CMOS image sensor have widely been used in a video camera, digital still camera, and the like. The image sensing apparatus has an image sensing region where a plurality of pixels including photodiodes are two-dimensionally arrayed.
As shown in FIG. 8, in an image sensing apparatus disclosed in Japanese Patent Laid-Open No. 2003-273342, as the distance from the center of the image sensing region increases, optical axes PAc, PAb, and PAa of light entering photodiodes PD in pixels incline more greatly from normal lines PLc, PLb, and PLa of the light receiving surfaces. To efficiently converge light on each photodiode PD in this image sensing apparatus, an on-chip lens 547 is arranged above the photodiode PD. Signal lines 544, 543, and 542 shifted along the inclination of the optical axis of light are interposed between the on-chip lens 547 and the photodiode PD in accordance with the distance from the center of the image sensing region to the pixel (the distance increases in the order of c, b, and a in FIG. 8). According to Japanese Patent Laid-Open No. 2003-273342, even if the optical axis greatly inclines from the normal line of the light receiving surface, light can reach the photodiode PD without losing it, improving the light receiving sensitivity of the photodiode near the peripheral portion of the image sensing region.
As shown in FIG. 9, in an image sensing apparatus (CCD image sensor) disclosed in Japanese Patent Laid-Open No. 2003-078125, a pixel spaced apart by a predetermined distance from the center of the image sensing region has a structure.
According to the technique disclosed in Japanese Patent Laid-Open No. 2003-078125, as the distance from the center of the image sensing region to the pixel increases, an optical axis PA of light entering a light receiving portion (photodiode) 605 inclines more greatly from a normal line PL of the light receiving surface. To efficiently converge light on the light receiving portion 605 in this image sensing apparatus, an on-chip lens 650 is arranged at a position along the optical axis PA above the light receiving portion 605. In the light receiving portion 605, impurity regions 605a to 605c are arranged to be shifted along the inclination of the optical axis PA of light in accordance with the distance from the center of the image sensing region to the pixel. According to Japanese Patent Laid-Open No. 2003-078125, smear by obliquely incident light near the peripheral portion of the image sensing region can be suppressed.
In the image sensing apparatus disclosed in Japanese Patent Laid-Open No. 2003-273342, as the distance from the center of the image sensing region to the pixel increases, regions CA1 to CA3 where light entering the photodiode PD is photoelectrically converted to generate electric charges are formed closer to the photodiodes PD of adjacent pixels, as shown in FIG. 8. Electric charges obtained by photoelectric conversion by the photodiode PD of a specific pixel may leak into the photodiode PD of a pixel adjacent to the specific pixel. That is, electric charges may leak into an adjacent pixel owing to obliquely incident light.
In the image sensing apparatus disclosed in Japanese Patent Laid-Open No. 2003-078125, it is considered that pixels in the image sensing region have the same positional relationship between the light receiving portion 605 and a channel stopper 609. In this case, as the distance from the center of the image sensing region to the pixel increases, a region where light entering the light receiving portion 605 is photoelectrically converted to generate electric charges may be formed closer to the channel stopper 609.
For example, in a pixel symmetrical within the image sensing region about the center of the image sensing region to the pixel shown in FIG. 9, it is considered that the optical axis inclines from the normal line PL of the light receiving portion 605 in a direction toward the channel stopper 609 (directional symmetrical to the optical axis PA in FIG. 9). In this case, obliquely incident light is photoelectrically converted in a region near the channel stopper 609 at the light receiving portion 605. Generated electric charges may leak into an adjacent pixel over a potential barrier formed by the channel stopper 609. In other words, electric charges may leak into an adjacent pixel owing to obliquely incident light.